Retarded cement



Patented Jan. 1, 1952 UNITED STATES PATENT OFFICE RETARDED CEMENT Norman C. Ludwig, Chicago, 111;, assignor to Universal Atlas Cement Company, a corporation 1 of Indiana Serial No.

- 1 r 2 Claims. (61. 106-93) This invention relates to cements having retarded rates of hydration or set, to slurries of such cement, and to the method of making these slurries. The cement with which the invention is concerned is a Portland or Portland-type cement.

Among the objects of the invention is the provision of a cement having a retarded rate of hydration, or a retarded set as it will be hereinafter termed, particularly at elevated temperatures such as are encoun er in the cementing of deep walls.

Further objects-ef'the invention reside in the provision of a slurry of the above cement, and in a method of making such slurry.

These and further objects of the invention will be more readily apparent in the following description.

In the cementing of oil wells it is customary to mix a hydraulic cement, for example a Portland or Portland-type cement, with the requisite amount of water to form a pumpable neat slurry, and to pump the mixture into the well and down the hole into the place where it is desired to have it harden. In present 011 well drilling practice, with wells commonly ranging from 6,000 to 12,000 feet or more in depth, high temperatures are encountered at the locations which are to be cemented, and relatively long periods of time are often required to pump the slurry into-place. Furthermore, in the customary practice of pumping the cement slurry down through the casing and either forcing it upward around the outer surface of the casing, or through perforations in the lower end of the easing into the formation sought to be sealed, the slurry is required to pass through narrow channels and small openings. Successful placement of the slurry, therefore, requires that the slurry shall, remain fluid and pumpable at high temperatiimr'sw'elal'hours before it begins to harden. However, after the slurry has been pumped into place, it is desirable to have the hydration or set proceed at" a rate at which the slurry will attain its final set and develop considerable strength within about 24 hours.

It has been found that Eortland and Rartlandtype cement slurries can e re arded so that cymee a eao ens or e satisfactory cementing of deep wells and like operations by the addition of hydroxyethylcellulgse (HEC) within certain deflate W More spec ca e cemen an slurry of the present invention contain hydroxyethylcellulose within the range of from .W by weight g; the dry cement. Ordinarily, it is preferred to use ydroxyethylcellulose within the range of from .05 to .50% by weight of the dry cement.

It has been found that when used in the above indicated amounts, hydroxyethylcellulose acts as a 'retarder at temperatures from i10.0m temperatuiejplzqilinbeing most effective in the temperature range of from 140 to 18012. W

Hydroxyethylcelluloseiwliich 'is sold commercially in powder form and also as an aqueous solution, is a hydroxyalkyl ether of cellulose.

Hydroxyetl'iylcellulose'is sometimfils'o termed glycol cellulose. It may be made by the reaction of ethylene oxide with alkali cellulose, the reaction apparently being one of addition and the product, hydroxyethylcellulose, being representable by the ormu a:

Hydroxyethylcellulose is soluble in water and 0 lar type used depending upon the particular It is to be understood,

mg of the 01 oye e em 10 ed may be any Portlapg q; figrtland-typgmdrauligpeigept the particuma be em application to be made of the cement or of the slurry, and of the properties demanded by such application, such as setting time, strength of the set slurry, and so forth. In making the test specimens of cements within the invention, the results of tests on which are set forth below, cements of both the A. S. T. M. Type I and Type II, Portland type, were employed as indicated. The oxide composition of such cements and the specific surface as determined by the Wagner turbidimetric method are given below:

Oxide composition-percent EXAMINER is readily soluble in water and which has In the tests of cements in accordance with the invention neat slurries containing the indicated type of cement, water, and the indicated additive were made up, there being used in each case ipeiteby..we htofth c me??? and partsby weight of water. This gave aslufiy which'wa's typical bf'thdse employed in oil well 1 cementing operations. The tests included the determination of the stiffening time of slurries at temperatures of 140, 180, 200, and 220 F..

the determination of the consistency of the slurries at intervals after their mixing, and the determination of compressive strengths of the set and cured cement structure resulting from such slurries. I

The stiiiening times and the consistencies of the slurries at temperatures of 140..180, and 200 F. were determined by use of an apparatus such as shown in Weller Patent'No. 2,122,765,

dated July 5, 1938, which is known as the Halliburton consistometer," and is designed to test stirring or p-umpability time of cement slurries at high temperatures. Such device consists essentually of a rotating cylindrical container with an internal paddle assembly fixed to a head whose movement is independent of the container. I With the container filled with cement slurry, the force against the paddle due to rotation of the container and the viscosity of the slurry is transferred from the head of the apparatus to a pendulum lever arm by asuitable connection. The

pendulum range is graduated from to divisions, representing slurry viscosities of 0 to 100 poises, a pull of 10 divisions on the pendulum is considered to represent the limit of pumpability of the slurry in an oil well. The temperature of the slurry during the test was maintained at the degree indicated by a thermostatically controlled bath surrounding the container. In the following tables st iifg n ingmtime was taken as the time from initiation of the test in the consistometer until the indicator on the pendulum showed a slurry viscosity of 100 pulses. ine ueterminatieir'm ifi stifiening time of slurries at a temperature of 220 F. was carried out by use of a pressure consistometer such as described in Technical Publication No. 1207 of the American Institute of Mining and Metallurgical Engineers. Such tests were conducted under pressure small enough so that they had little effect on the stiffening times and were sufficient only to prohibit evaporation of water from the slurry at the constant temperature of 220 R, which, of course, is above the boiling point of water. In such pressure consistometer the cell which contains the slurry is placed in a heated pressure cylinder and petroleum oil is pumped into the cylinder entirely surrounding the cell. At 220 F. it was necessary to subject the slurry tween the slurry and the oil. The apparatus works on the 'same principle as does the Halliburton consistometer, but the standard method for operation of the pressure consistometer, which method was employed in the present tests, specifies a shearing rate of 47 R. P. M. and viscosity of 80 poises for termination of the test, such shearing rate being about twice that employed in the Halliburton consistometer which as above pointed out, employs a viscosity of 100 poises for termination of the tests therein. At temperatures of 200 F. and lower, final stiffening times on the same slurries in the Halliburton Consistometer and the pressure consistometer check very closely.

The compressive strengths reported in the tables below were determined by making two-inch cubes which were molded from portions of the various cement slurries. When the molds were filled they were covered with metal plates and placed in the water of temperature baths operating at 140 and 200 F., as indicated. At approximately hours the specimens were removed from the molds and returned to the temperature baths. Three cubes of each slurry were broken at 24 hours and three were broken at three days by subjecting them to compression to destruction in a standard compression testing machine.

Hydroxyethylcellulose can be added to the dry in; cement in powder form and intermixed therewith before the addition of water to form the slurry,

or it can be added to the cement slurry in aqueous solutions. The more practical method, from a commercial standpoint, is to add the material 155 to the dry cement, and it was this method which was employed in making the tests. In cement slurries, especially when the slurr es are mge rapidly andc'oiisequently with high agitation, hy-

droxyethylcellulose acts as a foam stabilizin 40 agent and causes mg en'hamggggt of a considera e amoun of air. In the usual method s o f 1 i or use in oil wells therefore,

the addition of hydroxyethylcellulose may cause foaming and frothing of the slurry which is generally considered undesirable in oil well cementins Operations W22 Wiping hydroxyethylcellulose can bennllified by the use of deioaming a xn su t; as a 0-. and i Such defoaming agents when used, are added in small amountsyirom .02 to .05% tributyl phosphate being typical, sufiicient to suppress the foaming and frothing tendencies of hydroxyethylcellulose on the slurry under the particular slurry mixing 6 and pumping conditions employed. In each of the slurries tested which contained hydroxyethylcellulose, 0.02% tributyl phosphate was added.

TABLE I Stifiening time at constant temperature Cement Additive-per cent Stlfl'ening Times at Temperatures Indicated- Hr. Min. Hr. Min. Hr. Min.

Essie:

8&32

more

to but from two to five pounds per square inch by means of the oil acting through the medium of the synthetic rubber diaphragm interpose be- The stiffening time results given in Table I show that hydroxyethylcellulose is a considerably more effective retarder at temperatures of 140 and 180 F. than at temperatures of 200 and 220 F. For some purposes the long stiffening times of slurries 2 and 4 at temperatures of 140 and 180 F. would be disadvantageous. Consequently, when the slurry is to be used at such lower temperatures, it is necessary to use smaller amounts of hydroxyethylcellulose if the stiffening time is not to be unduly prolonged.

the cured cement structure resulting from the slurry, and in most instances, increases such strength both in structures cured at 140 F. and those cured at 200 F., over those resulting from similar slurries not containing hydroxyethylcellulose. The compressive strengths given in Table IV are the average values for three twoinch cubes cured and tested as set out above.

TABLE II Stifiening time at 140 F,

Stifienirag Fine at 14 Additive-per Cement cent Hr. Min.

1. Type II 0.15 HEC 7 10 2. Type II 0.05 HEC 3 14 As pointed out above, it is desirable in oil well cementing and like operations that the slurry remain easily pumpable over extended periods of time, even though it is subjected to high temperatures. The following Table III gives the results of slurry consistency tests run in the Halliburton Consistometer at a temperature of 200 F.

Whereas I have disclosed preferred compositions of the cement, cement slurries, and methods of making them, it is to be understood that the invention is capable of considerable variation as to details. I, therefore, claim as new the 3 ollowing:

1. A cement capable of forming a fluid slurry when mixed with water, said cement having a retarded set at temperatures above atmospheric, said cement consisting of a hydraulic cement mixed with from .05 to .60% water soluble hydroxyethylcellulose by weight of the dry cement.

2. A cement capable of forming a fluid slurry when mixed with water, said cement having a retarded set at temperatures above atmospheric, said cement consisting of a hydraulic cement mixed with from .05 to .60% water soluble TABLE III Slurry consistency at 200 F.

Consistency in Poises" at Times Indicated- Stiflenlng Time Cement Additivk per cent 15 min. 30 min. 1 hr. 2 hr. 3 hr. 4 hr. Hr. Min.

1 pc IL... None 14 19 20 1 29 2 Type 11.... HEC 0.25..." 15 20 19 1s 18 1e 5 37 3 Type I None 20 33 0 42 Type I HEC 0.60 .L.. 17 28 12 12 14 18 4 It may be seen from the above table that slurcement, respectively, with no hydroxyethylcellulose added, hydrated at such rates that slurry 1 had stiffened sufficiently so that it had a consistency of 100 poises at 1 hour and 29 minutes, and that slurry 3 had stiffened sufficiently so that it had a consistency of 100 poises at 42 minutes, thus showing that they were unfit for the cementing operations contemplated at 200 F. With both slurries 2 and 4, however, a consistency far below 100 poises was maintained throughout the entire period from the time of mixing to four hours after mixing, showing that such slurries remained pumpable for times which were adequate for cementing even the deepest wells.

The presence of hydroxyethylcellulose in the slurries in amount taught by the invention does hydroxyethylcellulose by weight of the dry cement and a defoaming agent.

MORNmN-C. LUDWIG.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,089,752 Lang Aug. 10, 1937 2,328,290 Neiderreither Aug. 31, 1943 2,398,047 Schmidt Apr. 9, 1946 2,427,683 Ludwig Sept. 23, 1947 7 2,432,971 Ruthman Dec. 16, 1947 2,476,306 King July 19, 1949 not in the main adversely affect the strength Q1 

1. A CEMENT CAPABLE OF FORMING A FLUID SLURRY WHEN MIXED WITH WATER, SAID CEMENT HAVING A RETARDED SET AT TEMPERATURES ABOVE ATMOSPHERIC, SAID CEMENT CONSISTING OF A HYDRAULIC CEMENT MIXED WITH FROM .05 TO .60% WATER SOLUBLE HYDROXYETHYLECELLULOSE BY WEIGHT OF THE DRY CEMENT. 